This invention pertains to an integrated circuit for automatically controlling the flesh tone in NTSC television receivers.
A circuit of this kind is disclosed in "IEEE Transactions on Consumer Electronics", 1979, pages 563 to 576, particularly pages 571 to 573. This circuit corrects each blue-minus-luminance signal value so that the angle included by the vector representing this value and the vector of the ideal flesh tone is halved. The electronic means for achieving this purpose is essentially an operational amplifier used as a voltage follower, and an additional operational amplifier, cf. FIGS. 17 and 18 on page 593 of the above reference. This prior art arrangement is thus suitable for NTSC television receivers equipped with conventional analog signal processing circuitry.
The present invention is directed to the problem of implementing automatic flesh-tone control in NTSC television receivers having digital signal processing circuitry. Digital NTSC television receivers are disclosed, for example, in the "Elektronik", Aug. 14, 1981, pages 27 to 35, and in the "Electronics", Aug. 11, 1981, pages 97 to 103.